[llvm] [AMDGPU] Expand constant named barrier matching in SDag (PR #191506)

[Matt Arsenault via llvm-commits]

================
@@ -35,6 +34,24 @@ define amdgpu_kernel void @kernel1(ptr addrspace(1) %out, ptr addrspace(3) %in)
 }
 
 
+define void @wakeup_barrier_null_bar() {
+; GFX1250-SDAG-LABEL: wakeup_barrier_null_bar:
+; GFX1250-SDAG:       ; %bb.0:
+; GFX1250-SDAG-NEXT:    s_wait_loadcnt_dscnt 0x0
+; GFX1250-SDAG-NEXT:    s_wait_kmcnt 0x0
+; GFX1250-SDAG-NEXT:    s_wakeup_barrier 0
+; GFX1250-SDAG-NEXT:    s_set_pc_i64 s[30:31]
+;
+; GFX1250-GISEL-LABEL: wakeup_barrier_null_bar:
+; GFX1250-GISEL:       ; %bb.0:
+; GFX1250-GISEL-NEXT:    s_wait_loadcnt_dscnt 0x0
+; GFX1250-GISEL-NEXT:    s_wait_kmcnt 0x0
+; GFX1250-GISEL-NEXT:    s_wakeup_barrier 0
+; GFX1250-GISEL-NEXT:    s_set_pc_i64 s[30:31]
+    call void @llvm.amdgcn.s.wakeup.barrier(ptr addrspace(3) null)
+    ret void
----------------
arsenm wrote:

```suggestion
  call void @llvm.amdgcn.s.wakeup.barrier(ptr addrspace(3) null)
  ret void
```

https://github.com/llvm/llvm-project/pull/191506